Occurrence of barley yellow dwarf virus (BYDV) isolates in different farmland habitats in western France and south-west England

The incidence and distribution of the three principal isolates of barley yellow dwarf virus (PAV, RPV and MAV) are described in winter cereal crops, cereal (stubble) regrowth and grasses from 11 sites in western France and south-west England during 1987 and 1988. Isolates were identified by indirect ‘sandwich’ ELISA using the monoclonal antibodies MAC91, MAC92 and MAFF2. More virus infection occurred in all localities and in most of the plant communities sampled, with the exception of perennial grass leys, in 1987 than in 1988. All three isolates were widespread. MAV was associated more with sites further north and PAV more with those further south. The geographical distribution of RPV was less variable. Underlying these trends, the relative abundance of isolates differed considerably between habitats. RPV always predominated in perennial grass leys and MAV in most cereal crops, although in the latter MAV was less prevalent in 1987 than in 1988. The greatest regional difference was found in stubble regrowth where PAV predominated in France but MAV predominated in England. Grasses from field margins (only sampled in England) were mainly infected by MAV and RPV. The implications of these findings for the epidemiology of BYDV are discussed, especially the roles of different host plant communities or habitats in the annual infection cycle of small-grain cereals.     

The effects of sowing date and choice of insecticide on cereal aphids and barley yellow dwarf virus epidemiology in northern England

During the mid-1980s, Sitobion avenae became recognised as an important vector of barley yellow dwarf virus (BYDV) in the Vale of York. A field trial at the University of Leeds Farm, North Yorkshire, was carried out during the autumn/winter of 1984-85 to evaluate different control procedures against S. avenae-transmitted BYDV and to investigate its epidemiology. Winter barley was sown on three dates in September, and plots were sprayed with either deltamethrin, demeton-S-methyl or pirimicarb on one of three dates between mid-October and mid-November, making a factorial design. Rhopalosiphum padi, the main vector of BYDV in southern England, were rarely found during the experiment, but the numbers of S. avenae were much higher, reaching a peak of 21% of plants infested in the unsprayed plots of the first sowing date. Single applications of each insecticide reduced populations of S. avenae to zero. Some treatments, particularly in the early sown plots and those treated with pirimicarb, however, did allow some recolonisation, and thus led to increased virus incidence and decreased yields. Sprays applied before the end of the migration of S. avenae were more efficient at controlling BYDV if the insecticide was persistent, otherwise a spray after this period, in November, was more effective. Virus incidence, although reduced by sprays, was generally low in plots sown on 18 and 27 September. In contrast, about 11% of plants were infected in unsprayed plots sown on 6 September and a small yield benefit was obtained with insecticidal treatments. Enzyme-linked immunosorbent assay (ELISA) of plants taken from the plots indicated that MAV- and PAV-like strains were present, and were most likely to have been transmitted by S. avenae.     

Effects of straw disposal and tillage on spread of barley yellow dwarf virus in winter barley

The effects of straw baling or incorporation, combined with ploughing, non-inversion tillage, or direct drilling on the incidence of barley yellow dwarf virus (BYDV), were investigated in plots of winter barley. Virus infection was more prevalent after ploughing (> 40% of the plot area damaged) than after non-inversion tillage (9 – 24%) or direct drilling (< 3%). For each cultivation method, more infection was associated with straw baling than with straw incorporation. There was a strong negative correlation between plot yields and the incidence of BYDV(r= -0.87). Monthly pitfall sampling of non-specific aphid predators showed that the population activity of several taxa (e.g. Linyphiidae, and the larger species of adult and larval Carabidae and Staphylinidae) declined for a short period in autumn-winter following cultivation. The overall treatment-ranking for numbers of predators in autumn (direct drilled > non-inversion > ploughed) was the opposite of subsequent virus infection. The possible roles of aphid predators and other biological mechanisms in determining the observed effects on BYDV, are briefly discussed.     

The barley yellow dwarf virus in Ukraine

Barley yellow dwarf virus (BYDV) has been identified in the Central region of the Ukraine. BYDV infection in winter wheat crops was shown to be highly harmful. There were no winter wheat cultivars being resistent to BYDV and tolerant cultivars occured rarely. In particular seasons BYDV may give rise to widescale epithoties.     

The occurrence of barley yellow dwarf viruses in CIMMYT bread wheat nurseries and associated cereal crops during 1988–1990

Enzyme-linked immunosorbent assay (ELISA)-based surveys of the occurrence of five barley yellow dwarf virus (BYDV) serotypes (MAV, PAV and SGV in “Group 1”; RPV and RMV in “Group 2”) in CIMMYT bread wheat nurseries and other small grain crops in various locations world-wide were undertaken in 1988, 1989 and 1990. The objective was to investigate the relative occurrence of BYDV serotypes in areas relevant to CIMMYT cereal breeding programs. Overall, MAV and PAV serotypes predominated in the samples collected, though their relative frequencies depended on the location. SGV serotypes were uncommon in most locations. Group 2 serotypes occurred widely, but RMV serotypes were more common than RPV serotypes.     

Transmission of barley yellow dwarf virus by field collected aphids (Homoptera: Aphididae) and their relative importance in barley yellow dwarf epidemiology in southwestern Idaho

Populations of cereal aphids were sampled from 1985–1988 and assayed for transmission of barley yellow dwarf virus (BYDV), Rhopalosiphum padi, Rho-palosiphum maidis, Sitobion avenae, Metopolophium dirhodum, Schizaphis graminum and Macrosiphum euphorbiae collected from host plants transmitted BYDV in bioassays. Of the 1028 Diuraphis noxia collected from plants, one may have transmitted BYDV. The isolate involved resembled SGV in serological and biological characteristics, but since it was not recoverable by any of more than 800 D. noxia subsequently tested, we suspect it may have been a contaminant. Among those aphids collected during the autumn from a suction trap adapted for live collection, R. padi transmitted BYDV most frequently. Other trapped species which transmitted BYDV included: R. maidis, Rhopalosiphum insertum, Macrosiphum euphorbiae, Metopolophium dirhodum and Ceruraphis eriophori. An adapted Infectivity Index indicated that R. padi is by far the most important vector of BYDV during the autumn sowing season in southwestern Idaho. Male R. padi consistently transmitted BYDV more frequently than did females collected during the same period.     

The effect of drought stress and temperature on spread of barley yellow dwarf virus (BYDV)

1 The effect of drought stress and temperature on the dispersal of wingless aphids Rhopalosiphum padi (L.) and the pattern of spread of BYDV (barley yellow dwarf virus) within wheat plants in controlled environment chambers was quantified. Combinations of three different drought stress levels, unstressed, moderate and high stress level, and three different temperatures, 5 ± 1 °C, 10 ± 1 °C, and 15 ± 1 °C, were investigated. 2 With increased temperature there was an increase in the mean distance of visited plants from the point of release and in the number of plants visited and infected with BYDV. Drought stress had no effect on mean distance moved by aphids at any temperature or on plants infected with virus at 10 °C and 5 °C. When plants were drought stressed, the numbers of plants visited and infected were greater at 15 °C than at 10 °C and 5 °C. 3 A greater proportion of plants visited by aphids was infected with BYDV when plants were stressed than when not stressed. At 15 °C a greater proportion of these plants was infected than at lower temperatures. There was no difference between treatments in the numbers of aphids present at the end of the experiment. 4 It is concluded that drought stress and temperature are of considerable importance in virus spread.     

Vector specificity of barley yellow dwarf virus serotypes and variants in southwestern Idaho

Plants with symptoms of barley yellow dwarf virus (BYDV) obtained in infection feeding assays of aphids collected in the field in Idaho between 1986 and 1988 were tested for virus transmissibility by possible aphid vectors. Isolates obtained during 1987–1988 were also tested with a range of polyclonal antisera which distinguished PAV, MAV, SGV, RPV and RMV serotypes. In 1989 some Idaho (ID) BYDV isolates, maintained as standards for comparison, were serotyped and tested for aphid transmissibility, using 11 species of aphids. There was not always the expected correspondence between serotype and vector specificity for ID isolates. For isolates obtained from field-collected Rhopalosiphum padi, vector transmissibility and serotype corresponded with previous reports; however, 44% of isolates which were serotyped as RMV were also transmissible by species other than Rhopalosiphum maidis. Similarly, the transmissibility of the ID laboratory standards did not always conform to the reported vector specificity of serotypes. The laboratory ID-MAV culture was transmitted by Metopolophium dirhodum and Myzus persicae as well as by Sitobion avenae. The laboratory ID-SGV culture was transmitted by R. padi and 5. avenae as well as by Schizaphis graminum. The ID-RPV culture was transmitted by S. graminum and Rhopalosiphum insertum as well as R. padi. Both of two laboratory ID-RMV cultures were transmissible by R. insertum and R. padi transmitted one of them. The results indicate that, for isolates collected in Idaho, vector specificity cannot be assumed from their serotypes.     

Assessing the risk of primary infection of cereals by barley yellow dwarf virus in autumn in the Rennes basin of France

In the Rennes basin, Rhopalosiphum padi is anholocyclic and represents more than 90% of suction trap catches of potential vectors of barley yellow dwarf virus (BYDV) during autumn. From 1983 to 1987 the possibility of predicting the risk of BYDV infection of batches of barley test seedlings (sampling units) exposed each week from September to December near a 12.2 m high suction trap was investigated. Three kinds of variables were checked as possible predictors: weekly mean or maximum temperatures; weekly catches of R. padi (including or excluding males); and percentage of sampling units infested by aphids. Three contrasting examples were observed: during the first three years (1983–1985), infection was high and its change with time followed temperature, aphid catches and plant infestation changes; in 1986, high numbers of aphids caught and a high proportion of plants infested resulted in only low infection and in 1987, both infestation and infection were very low. Simple linear regression analysis showed that the more reliable predictors of infection were the proportion of infested plants and to a lesser extent the numbers of trapped aphids. Multiple linear regressions including either of the three groups of ‘predicting’ variables did not result in any improvement in the prediction. At a practical level, the use of counts of aphid catches would seem a better compromise between accuracy and consistency of prediction and ease of gathering data than that of plant infestation but any significant improvement of the prediction should be sought in an early estimate of the amount of virus available to aphids before they colonise the plants.     

Development and characterization of a new barley yellow dwarf virus (BYDV)-resistant wheat germplasm

A barley yellow dwarf virus (BYDV)-resistant line HG295 was selected from a cross between cv. 77-5433 and Zhong 5 after extensive investigation in field, greenhouse and ELISA. Cytological analysis revealed that it was an euploid line and genetically stable. The existence of alien DNA in HG295 was identified by RAPD and Southern hybridization analyses showed that the alien DNAs came from Zhong 5 or Th. intermedium. The differences of BYDV resistance between L1 and HG295 are discussed.     

Nucleotide sequence of coat protein gene for GPV isolate of barley yellow dwarf virus and construction of expression plasmid for plant

GPV is a Chinese serotype isolate of barley yellow dwarf virus (BYDV) that has no reactionwith antiserum of MAV, PAV, SGV, RPV and RMV. The sequence of the coat protein (CP) of GPV isolate of BYDV was identified and its amino acid sequence was deduced. The coding region for the putative GPV CP is 603 bases nucleotides and encodes a Mr 22218 (22 ku) protein. The same as MAV, PAV and RPV, GPV contained a second ORF within the coat protein coding region. This protein of 17024 Mr (17 ku) is thought to correspond to the Virion protein genome linked (Vpg). Sequence comparisons of the CP coding region between the GPV isolate of BYDV and other isolates of BYDV have been done. The nucleotide and ammo acid sequence homology of GPV has a greater identity to the sequence of RPV than those of PAV and MAV. The GPV CP sequence shared 83.7% of nucleotide similarity and 77.5% of deduced amino add similarity, whereas that of the PAV and MAV shared 56.9%. 53.2% and 44.1%. 43.8% respectively. According to BYDV-GPV CP seque     

The effect of temperature and inoculation access period on the transmission of barley yellow dwarf virus byRhopalosiphum padi (L.) and Sitobion avenae (F.)

Winged individuals of Rhopalosiphum padi and Sitobion avenae transmitted the PAV-like and MAV-like isolates of barley yellow dwarf virus respectively. Success of transmission after inoculation access periods of 2, 6, 12, 24, 48 and 72 h were examined and survival, reproduction and movement of the aphid vectors were recorded at these times. The experiment was done at four different temperatures: 6^oC, 12^oC, 18^oC and 23^oC. For both isolates the inoculation efficacy did not increase after a 24 h inoculation access period and there was no difference in inoculation efficiency at the three highest temperatures, that at 6^oC being significantly lower than at 12^oC to 23^oC. The results suggest that autumn temperature is a critical factor for BYDV epidemiology in Britain with a small increase in autumn temperature leading to greatly increased infection rates.     

The effect of cereal break crops on barley mild mosaic virus

The effects of growing one, two or three years of resistant barley or winter wheat on barley mild mosaic virus were studied in experiments on two naturally-infested sites in Gloucestershire and Cambridgeshire. Disease incidence and yield of the susceptible cultivars Igri and Maris Otter following a three year break were not significantly different from those of control plots that had grown continuous susceptible barley. The effects of cropping sequence treatment on soil populations of the fungus vector, Polymyxa graminis, were assessed by estimating most probable numbers of propagules following bioassays. Variability was large and neither total numbers of propagules, nor those carrying virus, was significantly affected by the cropping treatments.     

Species composition of aphid vectors (Hemiptera: Aphididae) of barley yellow dwarf virus and cereal yellow dwarf virus in Alabama and western Florida

Yellow dwarf is a major disease problem of wheat, Triticum aestivum L., in Alabama and is estimated to cause yield loss of 21-42 bu/acre. The disease is caused by a complex of viruses comprising several virus species, including Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV. Several other strains have not yet been classified into a specific species. The viruses are transmitted exclusively by aphids (Hemiptera:Aphididae). Between the 2005 and 2008 winter wheat seasons, aphids were surveyed in the beginning of each planting season in several wheat plots in Alabama and western Florida Collected aphids were identified and bioassayed for their yellow dwarf virus infectivity. This survey program was designed to identify the aphid species that serve as fall vectors of yellow dwarf virus into winter wheat plantings. From 2005 to 2008, bird cherry-oat aphid, Rhopalosiphum padi (L.); rice root aphid, Rhopalosiphum rufiabdominale (Sasaki); and greenbug, Schizaphis graminum (Rondani), were found consistently between October and December. The species of aphids and their timing of appearance in wheat plots were consistent with flight data collected in North Alabama between 1996 and 1999. Both R. padi and R. rufiabdominale were found to carry and transmit Barley yellow dwarf virus-PAV and Cereal yellow dwarf virus-RPV. The number of collected aphids and proportion of viruliferous aphids were low. Although this study has shown that both aphids are involved with introduction of yellow dwarf virus to winter wheat in Alabama and western Florida, no conclusions can be made as to which species may be the most important vector of yellow dwarf virus in the region.     

Aerial flow of barley yellow dwarf viruses and of their vectors in western France

During the years 1989–1992 cereal aphids were caught alive in a low level (1.5 m high) suction trap operated in Le Rheu (Brittany, France) and tested for BYDV transmission. In most cases comparisons with data collected simultaneously by a 12.2 m suction trap operating in the same site resulted in good relationships between weekly catches at both heights. Results from transmission tests showed that: (i) the two main BYDV vectors were Rhopalosiphum padi and Metopolophium dirhodum during the years of experiment; (ii) PAV and MAV were the commonest viruses and RPV was relatively scarce; (iii) during spring M. dirhodum appeared to be the most important MAV vector and nearly as good a PAV vector as R. padi; (iv) during autumn R. padi was the only vector of the three viruses with mixed transmission allowing it to transmit also MAV probably by heteroencapsidation. To give an indication of the risk of infection, infectivity indices were calculated by multiplying the numbers of aphids caught by the 12.2 m suction trap by the proportion that were infective. These infectivity indices agreed with field records of primary infections.     

Host plant preference of cereal aphids in the field in relation to the ecology of barley yellow dwarf virus

Observational data obtained by exposing Avena sativa L., Phleum pratense L., Lolium perenne L., Poa pratensis L., and Zea mays L. to the aerial aphid population indicated food plant preference as resulting in a greater number of settlers on the preferred host, on which migrants also remained longer and deposited more nymphs than on the less suitable hosts. This behavioural pattern of alate Rhopalosiphum padi-fitchii is discussed in relation to the epidemiology of barley yellow dwarf virus disease.

---

Zusammenfassung Die Besiedlung gewisser Gräserarten durch geflügelte Blattläuse ist verschiedentlich als Ausgangspunkt von Epidemien der Gelbverzwergungsvirose der Gerste (Rotblättrigkeit des Hafers) diskutiert worden. Ziel der vorliegenden Arbeit war es daher, den unterschiedlichen Befall von Hafer, deutschem Weidelgras, Wiesenlieschgras, Wiesenrispengras und Mais durch Blattläuse des Rhopalosiphum padi-fitchii Komplexes täglich oder mehrstündlich in einem Freilandbeet abzulesen. Dabei zeigte es sich, dass der Hafer von den Blattläusen vorgezogen wurde und es auf diesem Wirt zur Ausbildung grösserer Kolonien kam als auf den Gräserarten, während Mais überhaupt nicht besiedelt wurde. Wirtspflanzen-präferenz manifestierte sich ausserdem dadurch, dass die gelandeten Geflügelten längere Zeit auf Hafer verbrachten als auf den offensichtlich weniger geeigneten Gräsern. Die Befunde werden im Zusammenhang mit der Epidemiologie der Gelbverzwergung besprochen.

     

Feeding behavior and transmission of barley yellow dwarf virus by Sitobion avenae on oats

Feeding behavior of Sitobion avenae F. (Homoptera: Aphididae) on oats (Avena sativa cv. Clintland 64) was electronically monitored, and waveforms corresponding to salivation, ingestion, and sieve element penetration described.During 90 min plant access, aphids ingested from phloem for 0–43 min (mean: 8.1 min) and non-phloem for 0–60 min (mean: 19 min). Only 65% of the aphids tested made phloem contact within 90 min, contacting phloem after 18–85 min (mean: 32 min). No significant difference was observed in the feeding behavior of aphids carrying barley yellow dwarf virus (BYDV) from that of non-viruliferous aphids.Penetration of a sieve element was a prerequisite for BYDV transmission but did not insure transmission. Penetration of one sieve element resulted in a 65% chance of transmission independent of the duration of phloem contact. The chance of transmission increased with increasing number of sieve element penetrations.Inoculation of oat seedlings with single, viruliferous aphids for 90 min is estimated to cause 54% of the plants to be infected. Also, it is estimated that no transmission can occur with plant access periods shorter than 17 min.

---

Zusammenfassung Das Probeverhalten von Sitobion avenae F. (Homoptera: Aphididae) auf Hafer (Sorte Clintland 64) wurden elektronisch verfolgt. Drei Wellenformen (S=Speichelfluss, X-das Eindringen in ein Siebelement, I=Nahrungsaufname) wurden registriert. In histologischen Untersuchungen wurden diese Wellenformen mit der Position der Stechborsten korreliert. Wenn X-Wellen oder eine X-I-Folge registriert wurden, war die Stechborste immer im Phloëm; bei S-Wellen oder bei einer S-I-Folge, war die Stechborste nie im Phloëm.Die Blattläuse wurden auf gesunden, fünf Tage alten Pflanzen während 90 Min beobachtet. 65% der Blattläuse erreichten nach 18–85 Min (Durchschnitt 32 Min) das Phloëm. Innerhalb 90 Min nahmen die Blattläuse während 0–43 Min (Durchschnitt 8.1 Min) Saft aus dem Phloem und während 0–60 Min (Durchschnitt 19 Min) Saft aus dem Mesophyll auf. Keine signifikanten Unterschiede im Probeverhalten wurden bei Blattläusen mit und ohne Barley Yellow Dwarf Virus (BYDV) festgestellt.Blattläuse, die innerhalb 24 Stunden BYDV übermitteln können, wurden für Übertragungsversuche verwendet. Das Probeverhalten dieser Blattläuser wurde manipuliert, und die Leistungsfähigkeit der Übertragung mit einer immunologischen Technik (ELISA) untersucht. Um BYDV zu übertragen mussten die Blattläuse mit einem Siebelement in Kontakt kommen. Nach der Stechborstenpenetration in ein Siebelement wurden 65% der Pflanzen mit BYDV infiziert. Der Prozentsatz infizierter Pflanzen und der Virusiter in den infizierten Pflanzen waren mit der Dauer der Siebelement-penetration (Anzahl von X-Wellen) nicht proportional. Wenn die Blattläuse mit zwei oder drei Siebelementen in Kontakt kamen, wurde der Prozentsatz infizierter Pflanzen signifikant erhöht, während der Virustiter nich verändert wurde. Infektionsprozente niedriger als 100% nach Siebelement-penetration sind möglicherweise das Resultat von Unterschieden in den Siebelementen.Es wird geschätzt dass 50% Infektion eintritt, wenn Pflanzen während ungefähr 83 Min von einer einzelnen infizierten Blattlaus besogen werden. Keine Übertragung von BYDV kann eintreten, wenn die Probezeit weniger als 17 Minuten beträgt.

     

Vectoring ability of aphid clones of Rhopalosiphum padi (L.) and Sitobion avenae (Fabr.) and their capacity to retain barley yellow dwarf virus

Vectoring ability of four aphid clones, Rp-M and Rp-R26 of Rhopalosiphum padi and Sa-R1 and Sa-V of Sitobion avenae, to transmit barley yellow dwarf (PAV, MAV and RPV) luteoviruses (BYDV) was compared in controlled conditions. Significant differences between highly efficient vectors (HEV), Rp-M and Sa-Rl, and poorly efficient vectors (PEV), Rp-R26 and Sa-V, were found in transmission of their specific viruses with acquisition and inoculation access periods (AAP, IAP) of 5 days. BYD-RPV was occasionally transmitted by both clones of S. avenae. None of 150 tested apterous adults of the Rp-R26 transmitted BYD-MAV, while 10% of transmission was observed from those of the Rp-M in a parallel test. An improved ELISA and immuno-PCR were adapted to test for viruses in aphids. The results obtained by the improved ELISA indicated there was a good correlation between virus detection in single aphids of HEV clones after a 5 day AAP and virus transmission by them. In contrast, the percentages of virus-carrying aphids of PEV clones were generally higher than those of their transmission rates. BYD-MAV and BYD-RPV were also detected by the improved ELISA in single aphids of their PEV clones, with the exception of BYD-RPV in those of Sa-V. However, after a 2-day IAP, the improved ELISA in most cases failed to detect these viruses in single aphids of PEV clones. Detection by immuno-PCR demonstrated that all three viruses could be acquired and retained by the aphids of both HEV and PEV clones. But, as visualised from electrophoretic bands, after the 2-day IAP the amplified products from aphid extracts of PEV clones were reduced. The detection in a batch of nine aphids by the improved ELISA revealed that virus content in PEV clones decreased more rapidly than that in HEV clones during transmission. Thus, the difference in transmission efficiency of the aphid clones within species was not caused by an inability to acquire virus, but was determined by variation in vectoring ability between them. This was due to differences in ability to prevent the passage of virions from haemocoel to salivary duct and/or different capacities for the retention of BYDV.     

A novel major gene on chromosome 6H for resistance of barley against the barley yellow dwarf virus

In a mapping population derived from the Ethiopian barley line L94 × Vada, natural infection by barley yellow dwarf virus (BYDV) occurred. While line L94 hardly showed symptoms, Vada was severely affected. The 103 recombinant inbred lines segregated bimodally. The major gene responsible for this resistance mapped to chromosome 6H. We propose to name the locus Ryd3. A subset of recombinant inbred lines, L94, and Vada were planted in a subsequent field test which confirmed the previous field observations. Double antibody sandwich enzyme-linked immunosorbent assays (DAS-ELISA) indicated that the epidemic was due to a combination of the serotypes BYDV-PAV and BYDV-MAV. In the accessions with the least BYDV symptoms no virus was detected, justifying the consideration of the gene as conferring true resistance rather than tolerance to these viruses. In a laboratory/gauze house trial a near-isogenic line carrying the Vada chromosome 6H fragment in an L94 background was affected as much as Vada. The effect of Ryd3 was quantified, and compared with that of the only other known major gene for resistance to BYDV, Ryd2, which is also of Ethiopian origin and is located on chromosome 3H. Both genes seemed to reduce the chance of the viral isolate used in this study to establish infection. In plants in which it became established, the virus concentration reached a similar level as in susceptible accessions, but with less dramatic symptom development. Inoculated plants in which the virus failed to multiply tended to show an increase in the number of ears per plant, resulting in higher grain yield per plant. Ryd3 co-segregates with several PCR-based molecular markers that may serve for marker assisted selection.     

Identification of polypeptide markers of barley yellow dwarf virus resistance and susceptibility genes in non-infected barley (Hordeum vulgare) plants

Summary Barley yellow dwarf (BYDV) is a group a closely related viruses which cause economic losses in a wide range of graminaceous species throughout the world. Barley plants can be protected from the effects of BYDV by the Yd2 resistance gene. Plants which contain the Yd2 gene also contain a constitutively expressed polypeptide which was not found in any plants without Yd2. Conversely, BYDV susceptible plants contain another constitutively expressed polypeptide which was not found in any of the BYDV-resistant lines examined. These two polypeptides appear to have the same molecular weight (as assessed by SDS-PAGE) and only slightly different iso-electric points. They also appear to contain an extensive range of similar antigenic determinants. Both polypeptides were found in F₁ hybrids made from resistant and susceptible plants. We suggest that these two polypeptides are the products of two allelic genes. Analysis of near-isogenic lines showed that the locus which controls the Yd2 resistance gene and the locus controlling the synthesis of the two polypeptides may be within ± 9 cM of each other. We have developed a Western blot technique which allows assessment of barley lines, 4-days after seed imbibition, for the presence of the Yd2 gene.